Transport and Gas Exchange in Plants and Animals

Comprehensive vocabulary flashcards covering plant transport systems (xylem, phloem, transpiration, translocation) as well as plant and animal gas exchange mechanisms across various taxa.

Cytoplasmic streaming

The active circulation of cytoplasm within and between plant cells through plasmodesmata, which transports large molecules and organelles such as chloroplasts.

Plasmodesma

A microscopic channel traversing the cell walls of adjacent plant cells that facilitates transport of molecules and direct intercellular communication.

Transpiration-cohesion-tension mechanism

The passive process driving water ascent in xylem, where evaporation of water from leaf mesophyll creates negative pressure (tension) that pulls a cohesive water column upward from roots.

Cohesion

The intermolecular attraction between molecules of the same substance, such as water molecules binding to one another through hydrogen bonds to form a continuous column in xylem tubes.

Adhesion

The intermolecular attraction between molecules of different substances, such as water molecules hydrogen-bonding to hydrophilic cellulose fibers within plant cell walls.

Capillary action

The tendency of water to rise within narrow-diameter conduits ($\sim 0.01\text{ mm} - 0.5\text{ mm}$ in xylem) due to the combined physical forces of cohesion, adhesion, and surface tension.

Sugar source

A plant organ that produces or releases more sugars than it consumes or stores, such as mature photosynthetic leaves or storage tubers in early spring.

Sugar sink

A plant organ that consumes or stores more sugar than it produces, such as growing roots, expanding shoots, developing fruits, or storage tubers during late summer and autumn.

Pressure-flow model

The mechanism of organic material translocation in phloem, where active loading of sucrose into sieve tubes draws water from xylem by osmosis, generating positive turgor pressure that pushes sap toward sink tissues.

Gas exchange

The biological process involving the physical uptake of environmental gases ($\text{O}_2$ or $\text{CO}_2$) into living cells and the reciprocal release of cellular waste gases into the surrounding environment.

Stoma

A microscopic pore primarily situated on the lower epidermis of leaves, flanked by two guard cells, that regulates evaporative water loss and photosynthetic gas diffusion ($\text{CO}_2$ influx and $\text{O}_2$ efflux).

Guard cells

Specialized paired epidermal cells flanking each stoma that regulate opening and closing by actively pumping $\text{H}^+$ out, driving $\text{K}^+$ influx down an electrical gradient, and swelling turgidly via osmosis.

Lenticels

Non-closing pores situated in the protective bark of woody stems, branches, and mature roots that allow continuous respiratory gas exchange for underlying living tissues.

Root hairs

Elongated, slender projections of root epidermal cells that vastly increase the absorptive surface area of young root tips for taking up water, dissolved minerals, and oxygen from soil air pockets.

Ventilation

The bulk flow or mechanical movement of a respiratory medium (either air or water) across a specialized gas exchange surface.

Gastrovascular cavity

A central digestive compartment with a single opening in cnidarians and flatworms that facilitates both digestion and direct diffusion-based gas exchange across tissue layers without a specialized circulatory system.

Tracheal system

A network of internal chitin-reinforced air tubes branching throughout the insect body that transports atmospheric oxygen directly to body cells independently of the circulatory system.

Tracheoles

The tiny, fluid-filled terminal branches of an insect tracheal system that contact individual body cells directly and serve as the respiratory exchange surface.

Spiracles

Small external pores positioned along the thorax and abdomen of an insect through which air enters and exits the internal tracheal system.

Countercurrent exchange

A respiratory arrangement in fish gills where blood flows through capillary lamellae in the opposite direction of incoming water flow, maintaining an $\text{O}_2$ concentration gradient along the entire pathway to extract $80\% - 90\%$ of dissolved oxygen.

Gill filaments

Thin, vascularized subdivisions projecting from gill arches in fish and aquatic amphibians that support capillary-rich lamellae as the primary site of gas exchange.

Positive pressure breathing

A ventilatory mechanism in amphibians (such as frogs) where lowering the floor of the mouth draws air through nostrils, followed by mouth floor elevation and nostril closure that pushes air under positive pressure into the lungs.

Parabronchi

Inelastic, microscopic parallel tubes within avian lungs across which continuous, unidirectional airflow travels and gas exchange occurs without tidal bidirectional mixing.

Avian air sacs

A system of eight to nine non-respiratory reservoirs in birds that expand and contract as mechanical bellows, driving unidirectional airflow through the parabronchi across two complete cycles of inhalation and exhalation.

Negative pressure breathing

The ventilatory mechanism in mammals where contraction of the diaphragm and intercostal rib muscles expands thoracic volume, dropping alveolar pressure below atmospheric pressure to pull air into the lungs.

Alveoli

Microscopic, cluster-like air sacs at the terminal ends of mammalian bronchioles surrounded by capillary networks, providing a thin, high-surface-area respiratory surface.

Two-way airflow

The tidal breathing mechanism found in mammals where fresh incoming air mixes with stagnant expired air retained in the respiratory tract, reducing the oxygen concentration gradient relative to unidirectional airflow systems.